/*
Copyright (C) 2021 by clash authors

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

package obfs

import (
	"bytes"
	"crypto/hmac"
	"crypto/rand"
	"encoding/binary"
	mathRand "math/rand"
	"net"
	"strings"
	"time"

	"libcore/clash/common/pool"
	"libcore/clash/transport/ssr/tools"
)

func init() {
	register("tls1.2_ticket_auth", newTLS12Ticket, 5)
	register("tls1.2_ticket_fastauth", newTLS12Ticket, 5)
}

type tls12Ticket struct {
	*Base
	*authData
}

func newTLS12Ticket(b *Base) Obfs {
	r := &tls12Ticket{Base: b, authData: &authData{}}
	rand.Read(r.clientID[:])
	return r
}

type tls12TicketConn struct {
	net.Conn
	*tls12Ticket
	handshakeStatus int
	decoded         bytes.Buffer
	underDecoded    bytes.Buffer
	sendBuf         bytes.Buffer
}

func (t *tls12Ticket) StreamConn(c net.Conn) net.Conn {
	return &tls12TicketConn{Conn: c, tls12Ticket: t}
}

func (c *tls12TicketConn) Read(b []byte) (int, error) {
	if c.decoded.Len() > 0 {
		return c.decoded.Read(b)
	}

	buf := pool.Get(pool.RelayBufferSize)
	defer pool.Put(buf)
	n, err := c.Conn.Read(buf)
	if err != nil {
		return 0, err
	}

	if c.handshakeStatus == 8 {
		c.underDecoded.Write(buf[:n])
		for c.underDecoded.Len() > 5 {
			if !bytes.Equal(c.underDecoded.Bytes()[:3], []byte{0x17, 3, 3}) {
				c.underDecoded.Reset()
				return 0, errTLS12TicketAuthIncorrectMagicNumber
			}
			size := int(binary.BigEndian.Uint16(c.underDecoded.Bytes()[3:5]))
			if c.underDecoded.Len() < 5+size {
				break
			}
			c.underDecoded.Next(5)
			c.decoded.Write(c.underDecoded.Next(size))
		}
		n, _ = c.decoded.Read(b)
		return n, nil
	}

	if n < 11+32+1+32 {
		return 0, errTLS12TicketAuthTooShortData
	}

	if !hmac.Equal(buf[33:43], c.hmacSHA1(buf[11:33])[:10]) || !hmac.Equal(buf[n-10:n], c.hmacSHA1(buf[:n-10])[:10]) {
		return 0, errTLS12TicketAuthHMACError
	}

	c.Write(nil)
	return 0, nil
}

func (c *tls12TicketConn) Write(b []byte) (int, error) {
	length := len(b)
	if c.handshakeStatus == 8 {
		buf := pool.GetBuffer()
		defer pool.PutBuffer(buf)
		for len(b) > 2048 {
			size := mathRand.Intn(4096) + 100
			if len(b) < size {
				size = len(b)
			}
			packData(buf, b[:size])
			b = b[size:]
		}
		if len(b) > 0 {
			packData(buf, b)
		}
		_, err := c.Conn.Write(buf.Bytes())
		if err != nil {
			return 0, err
		}
		return length, nil
	}

	if len(b) > 0 {
		packData(&c.sendBuf, b)
	}

	if c.handshakeStatus == 0 {
		c.handshakeStatus = 1

		data := pool.GetBuffer()
		defer pool.PutBuffer(data)

		data.Write([]byte{3, 3})
		c.packAuthData(data)
		data.WriteByte(0x20)
		data.Write(c.clientID[:])
		data.Write([]byte{0x00, 0x1c, 0xc0, 0x2b, 0xc0, 0x2f, 0xcc, 0xa9, 0xcc, 0xa8, 0xcc, 0x14, 0xcc, 0x13, 0xc0, 0x0a, 0xc0, 0x14, 0xc0, 0x09, 0xc0, 0x13, 0x00, 0x9c, 0x00, 0x35, 0x00, 0x2f, 0x00, 0x0a})
		data.Write([]byte{0x1, 0x0})

		ext := pool.GetBuffer()
		defer pool.PutBuffer(ext)

		host := c.getHost()
		ext.Write([]byte{0xff, 0x01, 0x00, 0x01, 0x00})
		packSNIData(ext, host)
		ext.Write([]byte{0, 0x17, 0, 0})
		c.packTicketBuf(ext)
		ext.Write([]byte{0x00, 0x0d, 0x00, 0x16, 0x00, 0x14, 0x06, 0x01, 0x06, 0x03, 0x05, 0x01, 0x05, 0x03, 0x04, 0x01, 0x04, 0x03, 0x03, 0x01, 0x03, 0x03, 0x02, 0x01, 0x02, 0x03})
		ext.Write([]byte{0x00, 0x05, 0x00, 0x05, 0x01, 0x00, 0x00, 0x00, 0x00})
		ext.Write([]byte{0x00, 0x12, 0x00, 0x00})
		ext.Write([]byte{0x75, 0x50, 0x00, 0x00})
		ext.Write([]byte{0x00, 0x0b, 0x00, 0x02, 0x01, 0x00})
		ext.Write([]byte{0x00, 0x0a, 0x00, 0x06, 0x00, 0x04, 0x00, 0x17, 0x00, 0x18})

		binary.Write(data, binary.BigEndian, uint16(ext.Len()))
		data.ReadFrom(ext)

		ret := pool.GetBuffer()
		defer pool.PutBuffer(ret)

		ret.Write([]byte{0x16, 3, 1})
		binary.Write(ret, binary.BigEndian, uint16(data.Len()+4))
		ret.Write([]byte{1, 0})
		binary.Write(ret, binary.BigEndian, uint16(data.Len()))
		ret.ReadFrom(data)

		_, err := c.Conn.Write(ret.Bytes())
		if err != nil {
			return 0, err
		}
		return length, nil
	} else if c.handshakeStatus == 1 && len(b) == 0 {
		buf := pool.GetBuffer()
		defer pool.PutBuffer(buf)

		buf.Write([]byte{0x14, 3, 3, 0, 1, 1, 0x16, 3, 3, 0, 0x20})
		tools.AppendRandBytes(buf, 22)
		buf.Write(c.hmacSHA1(buf.Bytes())[:10])
		buf.ReadFrom(&c.sendBuf)

		c.handshakeStatus = 8

		_, err := c.Conn.Write(buf.Bytes())
		return 0, err
	}
	return length, nil
}

func packData(buf *bytes.Buffer, data []byte) {
	buf.Write([]byte{0x17, 3, 3})
	binary.Write(buf, binary.BigEndian, uint16(len(data)))
	buf.Write(data)
}

func (t *tls12Ticket) packAuthData(buf *bytes.Buffer) {
	binary.Write(buf, binary.BigEndian, uint32(time.Now().Unix()))
	tools.AppendRandBytes(buf, 18)
	buf.Write(t.hmacSHA1(buf.Bytes()[buf.Len()-22:])[:10])
}

func packSNIData(buf *bytes.Buffer, u string) {
	len := uint16(len(u))
	buf.Write([]byte{0, 0})
	binary.Write(buf, binary.BigEndian, len+5)
	binary.Write(buf, binary.BigEndian, len+3)
	buf.WriteByte(0)
	binary.Write(buf, binary.BigEndian, len)
	buf.WriteString(u)
}

func (c *tls12TicketConn) packTicketBuf(buf *bytes.Buffer) {
	length := 16 * (mathRand.Intn(17) + 8)
	buf.Write([]byte{0, 0x23})
	binary.Write(buf, binary.BigEndian, uint16(length))
	tools.AppendRandBytes(buf, length)
}

func (t *tls12Ticket) hmacSHA1(data []byte) []byte {
	key := pool.Get(len(t.Key) + 32)
	defer pool.Put(key)
	copy(key, t.Key)
	copy(key[len(t.Key):], t.clientID[:])

	sha1Data := tools.HmacSHA1(key, data)
	return sha1Data[:10]
}

func (t *tls12Ticket) getHost() string {
	host := t.Param
	if len(host) == 0 {
		host = t.Host
	}
	if len(host) > 0 && host[len(host)-1] >= '0' && host[len(host)-1] <= '9' {
		host = ""
	}
	hosts := strings.Split(host, ",")
	host = hosts[mathRand.Intn(len(hosts))]
	return host
}
